The officer leading the investigation into the murder of Detective Garda Adrian Donohoe has said five people were involved in the gang responsible for the attack.
However, only one person fired the fatal shot.
Det Garda Donohoe was shot dead on 25 January during an armed raid on the Lordship Credit Union in Bellurgan, Co Louth.
The car used by the gang was found burnt out in south Armagh at 10.30pm - an hour after the murder.
Gardaí said a child's car seat, which was in the car when it was stolen, was not in the car at the time of the robbery and murder two days later.
They are trying to track down anyone who knows where the car seat is or who may have bought it or had it given to them.
Gardaí also said they recovered a specialist hammer which was used by the gang and are trying to trace its origin.
Assistant Commissioner Kieran Kenny insisted that there has been no reduction in personnel or resources in the investigation.
He said 800 people have been interviewed and over 2,300 lines of inquiry are being pursued.